The research in this program project in cellular developmental neurobiology is concerned with determining the genetic and environmental factors which influence the form and function of neurons. Emphasis on form as contrasted to function differs among the several project of the program. Nevertheless, there is consideration of the hypothesis that during development there is a continuous interaction between the determinants of form and function, and it is these interactions which are essential for the realization of the properties of the final differentiated neuron. Some of the proposed research involves a direct study of the developing nervous systems of tadpoles and fruitflies, while other projects examine regenerating neurons in cockroaches and snails, squid axons, and paramecia as models for development. The vertebrate systems being investigated consist of discrete sets of cells, whereas the invertebrate ones contain individual identified cells. The experimental approaches range widely, including electrophysiology, computer modelling, anatomy at the level of both light and electron microscopes, biochemistry, genetic modification, and in vitro tissue culture.